1. Field of the Invention
The present invention relates to a method of inspecting an inkjet head and the inspected inkjet head.
2. Description of the Related Art
It is generally known that in the process of manufacturing inkjet heads, the head characteristics, such as driving waveforms and driving voltages, tend to vary due to the differences in the lots of piezo-electric members, the manufacturing variations, etc. Therefore, not only the inkjet heads of one head manufacturing lot have different driving waveforms and different driving voltages from those of the inkjet heads of another head manufacturing lot, but also each individual inkjet head may have different characteristics from those of another inkjet head. In many cases, there is only one setting rank in regard to the driving waveforms of inkjet heads. If an inkjet head has a driving waveform that does not fall within this predetermined setting rank, it cannot be shipped as a commercial product. If piezoelectric members of one lot have characteristics that do not fall within a predetermined setting rank, they can be merely used as top plates, and the manufacturing efficiency therefore deteriorates. As a result, the inkjet heads are inevitably costly.
In a method of measuring the driving waveform and driving voltage of an inkjet head, it is known to fill colorless ink, oil ink, ultraviolet ink or the like into the inkjet head. Since the colorless ink does not contain dyes or pigments, it can provide improved preservation, stability and cleaning characteristics. It is for this reason that some manufacturers use the colorless ink. In many cases, the inkjet heads are not merely tested as to their driving waveforms and driving voltages; they are tested as to their printing characteristics as well because whether the ink is jetted properly and whether the direction in which the ink is jetted are evaluated by actually jetting the ink. In order to accurately evaluate the printing characteristics of the inkjet heads, the evaluation should be based on actually printed samples, but the colorless ink does not enable this evaluation. On the other hand, the ultraviolet ink and the oil ink enable measurement of the driving waveform and the driving voltage, and enable printing tests as well because they can be printed on sheets of paper in a recognizable way. Despite this, however, the ultraviolet ink and the oil ink are undesirable in that they cannot be easily cleaned after the inspection. If the interior of an inkjet head is not perfectly cleaned, the ultraviolet ink or the oil ink may be left as stains inside an ink supply tube. Moreover, different users, who use the inkjet heads, use different kinds of ink for recording images. If the printing test requires the same kinds of ink as the users use, the efficiency of the test may be very poor.
Under the circumstances, there is a need for an inkjet head inspection method that enables the driving waveform and the driving voltage to be properly determined with high efficiency during the inspection at the time of shipment.